Re: documentation clarification
Robert Wolfe (rwolfe++at++dciem.dnd.ca)
Fri, 11 Dec 1998 16:24:03 -0500
Angus Dorbie wrote:
>
> Robert Wolfe wrote:
> >
> > Hi,
> >
> > I am fairly certain that there is an error in the following
> > paragraph of manpage doc from pfNode.
> > Can somebody identify the error please ?
> >
> > //////////////////////////////////////////
> > The transformation of a pfDCS affects all its children. As the
> > hierarchy is traversed from top to bottom, each new matrix is pre-
> > multiplied to create the new transformation. For example, if DCSb
> > is below DCSa in the scene graph, any geometry G below DCSa is
> > transformed as G*DCSb*DCSa.
> > /////////////////////////////////////////
> >
> > What then would be the correct order of multiplication of a point
> > defined in the local coordinate system of the geometry G with the
> > parent DCSs in order to produce the point in world coordinates ?
> >
> > (My guess is G*DCSb*DCSa if I have correctly identified the error
> > above).
>
> But this is what is stated above, there is no error. You are correct
> about the object to world xform. This paragraph is discussing
> *modelling*
> transformation which is what DCS' & SCS' do, modelling transformation
> converts from object to 'world' coords. In OpenGL it is concatenated
> with viewing transformation, but performer hides this.
>
> I don't really understand your confusion, you seem to understand the
> transformation process.
>
I expected the example above to say "any geometry G below DCSb" which I
still believe is what is meant. Otherwise, how do you know what the
relationship between DCSb and any geometry below DCSa?
The other thing I am confused about is the order of application of
the DCS matrices to the geometry G to bring its vertices, say, from
their local face-value values to the global coordinate system above
DCSa in the scene graph. I don't understand the above notation
'G*DCSb*DCSa' and its relationship to pre-multiplication.
Does this mean that I could transform G vertices in the following
order:
pfVec3 Gvertex;
Gvertex.xformPt(Gvertex, *(DCSbPtr->getMatPtr()));
Gvertex.xformPt(Gvertex, *(DCSaPtr->getMatPtr()));
Thanks
Robert
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on Fri Dec 11 1998 - 13:28:56 PST